Chlorine Dioxide ("ClO.sub.2 ") has been incorporated in polymer [JP 63,296,758, NOK Corp, 1988; CA 111 P120181s] and ceramic beads [JP 63,274,434, Enkler Busin.K. K., 1988; CA 111 Pl1975h], and in a calcium silicate wrapped in non-woven cloth [JP 57,168,977, Enkler Busin.K. K., 1982; CA 98 P77552]to be used as a deodorant. Food preservation is an application where a gel form is preferred [JP Patent, Diamaru Kogyo Kaishi, Ltd., 1982; CA 97 22409]. Chlorine dioxide generating gels have also been used as topical applications for disinfection [A. J. Kenyon, S. G. Hamilton and D. M. Douglas, Am.J.Vet. Res., 45(5), 1101 (1986)].
Most attempts to generate chlorine dioxide involve acidification (and or chlorination) of a aqueous solution of chlorite, acidification (and/or reduction) of chlorates ["Comprehensive Inorganic Chemistry, The Halogens", Vol 3, R. C. Brasted, D. Van Nostrand Co., New York, 1954, p134-142] or reduction of a chlorite solution with aldehydes [U.S. Pat. No. 2,323,594, Mathieson Alkali Works, 1943]. Typically the preparation involves mixing component A (gel with suspended NaClO.sub.2) with component B (gel with lactic acid) immediately prior to use. .alpha.-hydroxy carboxylic acids (citric, tartaric, malic, glycolic) are especially useful for generating ClO.sub.2 by the reaction: EQU H.sup.+ +NaClO.sub.2 .fwdarw.HClO.sub.2 +Na.sup.+ EQU 5HClO.sub.2 .fwdarw.4ClO.sub.2 +HCl+2H.sub.2 O 1)
[Ger. Offen. 2,817,942, H.Allinger, 1979; PCT Int. Appl. WO, J. Mason, 1988, CA 110 P98205h]. Alternatively, NaClO.sub.2 and lactic acid have been separately encapsulated in polyvinyl alcohol and then mixed with water to generate C10.sub.2 [Can. 959,238, Chemical Generators, 1974]. Formulations involving sulfonic acids are also available [Europ. Pat. Appl. EP 287,074, Alcide Corp., 1987; CA 111 P45299f].
Another method for the production of chlorine dioxide employs acetic anhydride in the reaction: EQU 2NaClO.sub.2 +(MeCO).sub.2 O+H.sub.2 O.fwdarw.ClO.sub.2 +NaCl+MeCOOH+H.sup.+
2) EQU +MeCOONa+O.sub.2
(The unbalanced proton takes part in reaction 1)
Interestingly prehydrolysis of the anhydride to acetic acid prior to the addition of chlorite produces no chlorine dioxide. Direct reaction of chlorite with anhydride in the presence of water is obviously important in the reaction [W. Masschelein, I and EC Prod. Res. and Dev., 6(2), 137 (1967)].
This work suggests the possibility of storing chlorite in a complex with an acid anhydride in a stable form until reaction with moisture liberates the chlorine dioxide [U.S. Pat. No. 2,482,134, R. Aston, 1949). Food packaging with the incorporated disinfectant, chlorine dioxide, brings up an important public health question pertinent to this practice: Does chronic ingestion of residual levels of disinfectants result in a significant genetic or carcinogenetic hazard to the human population. It is clear from published pharmacokinetic studies aided by incorporation of a chlorine radioisotope (.sup.36 Cl) that skin patch (Alcide gel) administration of chlorine dioxide and chlorite result in prolonged systemic residence of chlorine containing residues [J. Scatina, M. S. Abdel-Rahman, S. E. Gerges, Y. Khan and O. Gona, Fund.Appl.Tox., 4, 479 (1984)].
Meier et. al. published a report on the effect of subchronic and acute oral administration of chlorine, chlorine dioxide, sodium chlorite, and sodium chlorate on the induction of chromosomal aberrations and spermhead abnormalities in mice [J. R. Meier, R. J. Bull, J. A. Stober and M.C. Cimino, Environ. Mutagenesis, 7, 201 (1985)]. Only the highly reactive hypochlorite resulted in a weak positive effect for mutagenic potential. The disinfectants failed to induce any chromosomal aberrations or increased numbers of micronuclei in the bone marrow of mice. Other hazards which have been associated with chlorine dioxide but were not incorporated in the published study include hemolytic anemia and hypothyroidism. One of the reasons for the relatively innocuous effect of ClO.sub.2 is its inability to produce halomethanes, unlike hypochlorite and chlorine [R. Vilagines et. al., Proc. AWWA Disinfect. Semin. 1977, paper 3, 24pp; CA 93 1735 13f].
In U.S. Pat. No. 4,585,482 has used the gradual hydrolysis of alternating poly (vinyl methyl ether-maleic arthydride) or poly (lactic-glycolic acid) to generate acid which can release chlorine dioxide from sodium chlorite. In the process a solution process is used to encapsulate a polyalcohol humectant and water with the polyanhydride or polyacid in a nylon coating. After sodium chlorite is permitted to diffuse into the capsule through the nylon wall, an impermeable polystyrene layer is coacervated around the nylon capsule. The capsules can be coated onto surfaces to release chlorine dioxide and provide biocidal action for several days to months.
Despite the many advantages of the '482 patent, there are some limitations. First, a large number of processing steps involving numerous chemical reactions and physical processes with disposal problems are required. Second, the chemistry is limited to batch processes. Third, a clear film cannot be produced. Finally, chlorine dioxide release starts immediately.